Difficulty: Moderately Easy
Special Method to Multiply Numbers Near Base 100
Step1
Multiple numbers that are close to 100 with this method. For this example example, multiply 95 x 81.
Step2
Subtract each number from 100. 100 - 95 = 5 and 100 - 81 = 19.
Step3
Arrange the numbers from Step 1 in the following manner:
95 5
81 19
Step4
Subtract crosswise either (95 - 19) or (81 - 5) to get 76, which is the first part of the answer. Then multiply vertically 19 X 5 = 95, which is the second part of the answer. The final answer is 7695.
Step5
Multiply numbers, which are just over 100, such as 105 X 103, by following Steps 2 through 4. For this example, you get:
105 5
103 3
Step6
Add crosswise either (105 + 3) or (103 + 5) to get 108. Then multiply vertically (5 x 3) to get 15. The final answer is 10815. Note that for numbers over 100, you add crosswise. For numbers just below 100 you have to subtract crosswise.
Method for Long Multiplication of Numbers
Step1
Multiply this example: 24 X 41. Imagine that 41 is directly below 24:
24
41
Step2
Start from the bottom right and multiply 4 X 1 = 4.
Step3
Multiply crosswise 1 X 2 = 2 and 4 X 4 = 16.
Step4
Add 2+16 = 18 from Step 3. Put down 8 and carry 1 over.
Step5
Multiply vertically 2 X 4 = 8 and add the carried over 1, so 8 + 1 = 9. The final answer is 984. You can use this method to solve long multiplications of any size. With practice, you'll be able to do these calculations mentally.
